Field
The present invention relates to an LED luminescence apparatus, and more particularly, to an LED luminescence apparatus which drives a plurality of LEDs in multistage using AC power in order to improve a power factor and a total harmonics distortion (THD) ratio, controls a current rising period and a current falling period of switches for use in multistage driving by varying the gate terminal voltages of the switches, controls current flowing to LEDs in consideration of variable characteristics of AC power, or drives the LEDs using voltage output from a phase control type dimmer.
Discussion of the Background
An LED (Light Emitting Diode) luminescence apparatus in the related art, which uses AC power, provides a unipolar ripple voltage which is output from a rectifying circuit that is implemented by a bridge circuit to high-voltage LEDs through resistors.
In the LED luminescence apparatus in the related art using AC power, LEDs emit light in a time period during which the AC voltage is higher than a forward voltage Vf of the LEDs, and current flows to the LEDs in a time period during which the LEDs emit light. Due to this, a phase difference occurs between the AC voltage (LED driving voltage) that is applied to the LEDs and the LED driving current, and thus the electrical characteristics of the LED luminescence apparatus using AC power, such as power factor and total harmonics distortion, may not satisfy the standards that are required in LED luminescence.
Further, a commercial AC power supply is unable to provide an AC voltage of an ideal sinusoidal waveform. That is, the commercial AC voltage has the problem that the level of the commercial AC voltage is higher or lower than a reference voltage of the ideal sinusoidal waveform, and due to such harmonic waves, the LED driving voltage has a waveform that is distorted from the sinusoidal waveform. Since the waveform of the LED driving voltage is distorted, the waveform of the LED driving current also becomes distorted.
According to the LED luminescence apparatus in the related art, since the waveform of the LED driving current is distorted, very large deviations occur in the luminescence efficiency of the LEDs.
On the other hand, a dimming function of a typical luminescence apparatus is a function that is used to control the brightness of the luminescence apparatus according to user's preference, and the adaptation of the dimming function has conventionally been greatly limited. At the present time, however, due to the increase of the use amount of electric energy, energy saving has become one of the most important issues. Accordingly, the dimming function of the luminescence apparatus, which was once an optional function simply for user's preference, has been highlighted as an essential function for saving electric energy.
The luminescence apparatus using AC power performs the dimming function by adjusting the effective voltage Vrms of the AC power through control of an AC phase of the AC power by using semiconductor elements such as triacs.
The luminescence apparatus in the related art, such as an incandescent light bulb and a halogen lamp, may have very low impedance since the characteristic of the equivalent circuit thereof is equal to that of a resistor circuit. The electrical characteristics of such an incandescent light bulb and a halogen lamp are suitable to the load characteristics that are required in the phase control type dimmer (dimmer using triac switches), and the brightness of the incandescent light bulb and the halogen lamp can be easily controlled by the voltage output from the dimmer.
However, the LED luminescence apparatus has various types of impedance depending on the level of the applied voltage due to the UV characteristics of the LEDs. Further, if the level of the input voltage of the LEDs is lower than the forward voltage Vf of the LEDs, current hardly ever flows, and thus the LED luminescence apparatus has very high impedance. Because of this, the LED luminescence apparatus has the problem that it is not easy to control the brightness of the LED luminescence apparatus by the voltage output from the phase control type dimmer.